The present invention relates to an anticollision system for an objective lens for use in an optical data reproducing apparatus for reproducing data from a data recording medium by using an optical signal. Examples of such apparatus are the compact disc and photomagnetic disc.
In recent years, an optical data reproducing apparatus has been highlighted widely for use in the industrial field because the data reproducing apparatus has large capacity and high reliability.
An example of a conventional optical data reproducing apparatus will be described hereinafter with reference to the drawings. FIG. 1 shows the structure of a conventional optical data reproducing apparatus. In FIG. 1, reference numeral 1 represents a data recording medium, and a signal is recorded on a recording surface thereof. Reference numeral 2 represents an objective lens which condenses light on a data recording surface of the data recording medium 1. Reference numeral 3 represents optical separation means which separates light transmitted toward the data recording medium 1 from light returning therefrom. Reference numeral 4 represents light emitting means which emits laser light. Reference numeral 5 represents data signal detecting means, reference numeral 6 represents focusing error signal detecting means, and reference numeral 7 represents objective lens driving means.
The operation of the optical data reproducing apparatus constructed as described above will be described hereinafter. First, laser light emitted from the light emitting means 4 passes through the optical separation means 3, and it is condensed by the objective lens 2 and focused on the data recording surface of the data recording medium 1. Light reflected from the data recording medium 1 returns again to the objective lens 2, and it is incident on the data signal detecting means 5, and on the focusing error signal detecting means 6, after it has been separated by the optical separation means 3. The focusing error signal detecting means 6 generates a positive or negative value signal, respectively, depending on whether the data recording medium 1 is positioned on one side of the objective objective lens 2 or on the opposite side thereof, and generates a signal of an amplitude proportionate to the relative distance from the focal point. Since the data recording medium 1, which is rotated by a spindle motor (not shown) produces a facial deflection due to its deformation or vibration, the objective lens 2 is made to follow the facial deflection of the data recording medium 1 by the objective lens driving means 7 by using a focusing error signal obtained by the focusing error signal detecting means 6 so that the objective lens 2 is just brought into focus on the recording surface of the data recording medium 1. At the same time, the data signal detecting means 5 reads a data signal recorded on the data recording medium 1 in the form of a light intensity variation.
In the above-described structure, however, there is a possibility such that, when a following operation for bringing the objective lens 2 into a focus on the recording surface of the data recording medium 1 fails or malfunctions for some reason, the objective lens 2 comes too close to the data recording medium 1 and they collide with each other in the worst case, thus causing the objective lens 2 or the data recording medium 1 to be damaged. In particular, in recent times, there is a tendency toward miniaturization of the optical data reproducing apparatus and the relative distance between the objective lens 2 and the data recording medium 1 is made small, so that the possibility will occur that such a collision, when the following operation fails or malfunctions, is more and more increased.